EXCHANGE 


-.^  •  -"     ..  -"•   .    .";  -  -'-'.  -'"- .  •    • 


Inter  molecular  Rearrangement  and 

Equilibrium   of   the   Normal   and 

I  so  Propyl  Bromides  and  Their 

Formation   from   Hydrogen 

Bromide  and  Propylene 


A  DISSERTATION 

PRESENTED   TO   THE   FACULTY  OF  BRYN  MAWR  COLLEGE 

IN  PARTIAL  FULFILMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


BY 
HELEN   GOLDSTEIN  RAFSKY 

1922 


E ASTON,  'PA.: 

ESCHBNBACH  PRINTING  COMPANY 
1922 


Intermolecular  Rearrangement  and 

Equilibrium   of   the   Normal   and 

I  so  Propyl  Bromides  and  Their 

Formation   from   Hydrogen 

Bromide  and  Propylene 


A  DISSERTATION 

PRESENTED    TO    THE    FACULTY  OF  BRYN  MAWR  COLLEGE 

IN  PARTIAL  FULFILMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


BY 
HELEN   GOLDSTEIN   RAFSKY 

1922 


EASTON,  PA.: 

ESCHENBACH  PRINTING  COMPANY 
1922 


CONTENTS 

Introduction 5 

I  Rearrangement  of  the  propyl  bromides,  and  equilibrium  in  the  gas- 
eous state 7 

Methods  employed  in  testing  the  mixed  bromides 9 

II  The  union  of  hydrogen  bromide  with  propylene 13 

Reaction  in  the  gaseous  state 

(a)  Equimolecular  quantities  of  propylene  and  hydrogen  bro- 
mide in  large  bulbs 14 

(b)  In  tubes  at  atmospheric  pressure  under  varying  conditions.  19 
Reaction  of  propylene  and  aqueous  hydrogen  bromide 

(a)  Gaseous  propylene  at  atmospheric  pressure 20 

(b)  Liquid  propylene  in  sealed  tubes 21 

III   Dissociation  of  the  propyl  bromides 23 

Preparation  of  materials 25 

Summary 26 


Intermolecular    Rearrangement   and    Equili- 
brium of   the  Normal  and  Iso  Propyl 
Bromides  and  Their  Formation  From 
Hydrogen  Bromide  and  Propylene 

From  time  to  time  theories  have  been  proposed  with  the 
hope  that  they  might  throw  some  light  upon  the  relation  which 
must  exist  between  the  chemical  constitution  of  organic  com- 
pounds and  their  physical  and  chemical  properties.  This  re- 
lation is  an  extremely  complex  one,  as  we  should  expect  if  we 
accept  Van't  Hoff's  view  that  each  atom  in  a  molecule  exerts 
an  influence  upon  every  other  atom  in  the  molecule,  both 
through  space  and  indirectly  through  the  intervening  atoms. 

This  problem  has  remained  unsolved  up  to  the  present.  It 
is  possible  that  some  headway  might  be  gained  by  a  thermo- 
dynamic  investigation  of  the  behavior  of  some  simple  organic 
compounds.  In  the  following  investigation  the  relative  sta- 
bilities of  the  monobrom  propanes  are  studied  and  it  is  now 
possible  for  the  first  time,  to  state  definitely  which  is  the  more 
stable.  It  is  of  great  importance  to  find  the  relation  between 
this  difference  in  stability  and  the  arrangement  of  the  atoms 
in  the  two  isomers. 

The  only  similar  case  which  has  been  investigated  is  that 
of  the  equilibrium  between  the  monobrom  derivatives  of  iso- 
butane.1 

Michael2  believed  that  that  compound  would  be  most  stable, 
in  which  the  bromine  atom  was  bound  to  the  carbon  atom  which 
was  must  strongly  under  the  influence  of  hydrogen  atoms. 
Michael's  scale  of  influence3  is  an  attempt  to  show  how  this 
influence  varies  with  the  relative  positions  of  the  atoms.  If 

1  Brunei,  Ber.,  44,  1000  (1911);    Ann.,  384,  245(1911);    /.  Amer. 
Chem.  Soc.,  39,  1978  (1917). 

Michael  and  Leupold,  Ann.,  379,  302  (1911). 
Michael  and  Zeidler,  ibid.,  393,  92  (1912). 

2  J.fiir.  prakt.  Chem.,  60,  286,  409  (1899). 

3  Ber.,  39,  2139  (1906). 


any  given  atom  is  numbered  1,  and  the  rest  of  the  atoms  are 
numbered  consecutively  to  show  their  degree  of  removal  from 
atom  1 ;  then  the  combined  direct  and  indirect  influence  upon 
atom  1  will  decrease,  according  to  Michael,  in  the  following 
order;  2-3-5-6-4-(9-10-ll)-8.  This  scale  was  derived  after 
a  study  of  a  great  number  of  reactions  which  had  previously 
been  investigated. 

As  was  shown  in  the  aforementioned  study  of  the  monobrom 

32  43 

H3C\   1  23  H3C\    23       1 

332  \CBr-CH3  43  \CH-CH2Br 

H3C/  H3C/ 

I  II 

derivatives  of  isobutane,  bromine  has  a  greater  tendency  to 
combine  with  the  tertiary  than  with  the  primary  carbon  atom. 
This  can  be  explained  by  the  fact  that  the  tertiary  carbon 
atom  (I)  has  nine  hydrogen  atoms  in  position  3,  while  six  of 
these  are  in  position  4  with  respect  to  the  primary  carbon 
atom  (II). 

In  the  case  of  the  propyl  bromides  Michael  had  concluded4 

231  23  34231 

CHa— CHBr— CH3  CHs—  CHr-CH2Br 

III  IV 

that  isopropyl  bromide  (III)  would  be  the  more  stable  because 
it  has  six  hydrogen  atoms  in  position  3,  while  in  the  normal  bro- 
mide (IV)  three  of  these  have  been  moved  to  position  4.  This 
conclusion  he  believed  was  confirmed  by  the  results  of  addition 
of  halogen  hydrides  to  alkenes. 

As  was  to  be  expected,  and  as  will  be  shown  below,  catalytic 
influences  determine  the  result  in  such  cases.  Conclusions 
regarding  stability  can  only  be  drawn  when  the  compounds 
concerned  can  be  obtained  in  a  state  of  equilibrium,  as  has  now 
been  done. 

4  J.furprakt.  Chem.  60,  447  (1899);  J.  Amef.  Chem.  Soc.,  32,  1004 
(1910). 


I*    Rearrangement  of  the  Propyl  Bromides,  and 
Equilibrium  in  the  Gaseous  State 

Aronstein5  showed  that  at  280°  C.  normal  propyl  bromide 
undergoes  rearrangement  to  isopropyl  bromide.  He  believed 
that  if  he  could  heat  the  normal  bromide  for  a  sufficiently 
long  time  and  to  a  sufficiently  high  temperature,  the  process 
of  isomerisation  would  eventually  go  to  completion  giving 
pure  isopropyl  bromide.  However,  he  later  found  that  the 
reaction  did  not  go  to  completion  even  after  heating  for  one 
hundred  hours.6  In  order  to  explain  this,  he  attempted  to  show 
that  isopropyl  bromide  changed,  partially  at  least,  to  normal 
propyl  bromide;  but  obtained  only  doubtful  evidence.  Fawor- 
sky,7  however,  succeeded  by  prolonged  heating  in  sealed  tubes 
at  250°  C.  and  repeated  removal  of  the  portion  isomerised,  in 
converting  about  20%  of  iso-  into  normal  propyl  bromide  and 
showed,  therefore,  that  this  is  a  reversible  reaction.  However, 
there  is  nothing  in  his  results  to  show  the  position  of  equilib- 
rium. 

Michael  and  Leupold8  found  that  isomerisation  was  notice- 
able at  184°  C.  They  heated  the  liquid  bromides  in  tubes  to 
237°  and  262°  C.  for  one  hour,  getting  17  to  20%  isopropyl 
bromide  from  the  normal  isomer,  but  they  found  that  the  re- 
arrangement of  iso-  to  normal  propyl  bromide  took  place  to 
only  an  immeasureably  small  extent.  Because  of  signs  of 
decomposition  these  experiments  were  not  continued  to  an 
equilibrium  point. 

It  can  now  be  stated  with  certainty,  as  shown  below,  that 
when  either  iso-  or  normal  propyl  bromide  is  heated  to  a  suffi- 
ciently high  temperature  we  get  dissociation  and  isomerisa- 
tion with  the  following  equilibria : 

CH3-CH2-CH2Br  ^  HBr  +  C3H6  ^  CH3-CHBr-CH3. 

Faworsky  (loc.  cit.}  believed  this  to  be  the  course  of  the  re- 
action, though  Michael  and  Zeidler9  believed  that  the  bromides 
could  change  directly  without  going  through  the  stage  of 

5  Ber.y  14,  607  (1881). 

6  Rec.  trav.  chem.,  1,  134  (1882). 

7  Ann.,  354,325  (1907). 
*Ibid.,  379,  263  (1911). 
9  Ann.,  393,  92  (1912). 


8 


B 


— -•£ 


B 


dissociation.     The  equilibrium  desired  is  the  ratio  of  the  two 

undissociated  bromides. 

In  the  present  investigation  this  ratio  is  obtained  by  heating 

the  bromides  until  equilib- 
rium has  been  reached,  then 
cooling  suddenly  and  analyz- 
ing the  products.  The  brom- 
ides are  thus  condensed  while 
the  dissociation  products 
escape.  The  experiments  be- 
low on  the  union  of  hydrogen 
bromide  and  propylene  show 
that  this  reaction  takes  place 
so  slowly  that  there  is  no 
danger  of  reunion  of  the  dis- 
sociation products  during  the 
cooling  process. 

The  procedure  followed 
was  to  heat  about  ten  grams 
of  the  bromide  in  large  glass 
tubes.  These  tubes  were  of 
heavy  pyrex  glass  of  3.3  cm. 
external  diameter  and  55  to 
75  cm.  long,  sealed  at  one 
end,  with  the  other  end  sealed 
to  a  0.5  mm.  capillary  tube. 
They  were  thus  sufficiently 
large  so  that  on  heating,  all 
of  the  bromide  would  be  con- 
verted into  vapor.  After  the 
introduction  of  the  bromide 
the  capillary  was  further 
drawn  down  to  a  tip  two  to 
three  inches  long,  of  extrem- 
ely fine  bore.  With  the  tube 
in  a  vertical  position,  the 
bromide  was  then  slowly 
boiled  so  as  to  expel  all  the 

air  from  the  tube.     The  upper  surface  of  the  bromide  vapor 

could  easily  be  followed  by  the   even    ring   of   condensation 


— 


which  gradually  crept  up  the  tube.  When  all  of  the  air  had 
been  removed  the  end  of  the  fine  capillary  was  sealed. 

These  tubes  were  heated  in  furnaces  for  varying  lengths 
of  time;  then  the  fine  capillary  was  inserted  into  a  specially 
constructed  and  particularly  efficient  brass  condenser,  Fig.  1, 
and  the  tip  broken  off.  The  inner  and  outer  chambers,  A  and  B, 
of  the  condenser  were  filled  with  ice  and  salt,  so  that  the  thin 
brass  walls  of  the  inner  chamber,  C,  were  well  cooled.  The 
gases  entered  at  D  and  were  given  a  spiral  motion  up  through 
the  condenser  by  the  partition  E.  The  condensed  bromides 
dripped  down  at  F,  into  a  flask,  while  the  hydrogen  bromide 
and  propylene  escaped  at  a  small  opening  in  G.  A  test  of  the 
temperature  of  the  gases  at  the  outlet  in  G  with  an  Anschutz 
thermometer  showed  it  to  be  13°  C.  Later  this  temperature 
was  followed  more  accurately  with  a  copper-constantan  thermo- 
couple and  was  found  to  range  from  8°C.  tolo°C. 

The  liquid  products  were  usually  freed  of  hydrogen  bromide 
and  dried  by  standing  over  anhydrous  potassium  carbonate; 
a  few  were  washed  with  water  and  dried  over  potassium  car- 
bonate for  a  few  minutes  only.  No  appreciable  difference 
was  found  in  these  results.  Furthermore,  as  evidence  that  there 
was  no  reaction  between  potassium  carbonate  and  the  bromides, 
specimens  of  the  pure  bromides  were  left  standing  with  the  car- 
bonate for  48  hours.  The  carbonate  was  washed  with  ether, 
dissolved  in  water  and  dilute  nitric  acid,  and  tested  with  silver 
nitrate  solution.  This  gave  no  greater  turbidity  than  a  blank 
test  with  the  original  potassium  carbonate.  Also,  repetition 
of  the  analysis  of  some  of  the  mixtures  after  standing  several 
months  with  potassium  carbonate  showed  no  alteration. 

Methods  Employed  in  Testing  the  Mixed  Bromides 

1.  Before  applying  any  quantitative  tests,  a  qualitative 
test  for  the  presence  of  a  normal  bromide  was  performed  with 
the  first  few  experiments  of  each  type  explained  in  this  paper. 
The  nitrolic  acid  or  pseudonitrole  was  formed  from  the  normal 
or  isopropyl  bromides  respectively  and  these  were  tested  accord- 
ing to  Richard.10  The  former  gives  a  yellowish  red  color  in 
alkaline  solution,  while  the  latter  gives  a  blue  color  in  acid  so- 

10  Ann.  de  Chem.  et  de  Phys.,  [8]  21,  341  (1910). 


10 

lution.     The  primary  nitro  compounds  also  give  copious  white 
precipatates  with  lead  acetate.11 

2.  The  refractivities  of  the  two  bromides  were  tested  at  25  °  C. 
with  a  Pulfrich  refractometer  and  it  was  found  that  the  re- 
fractivities of  mixtures  of  the  two  isomers,  plotted  against  the 
percentage  composition,  fell  on  a  straight  line.     Before  testing 
any  of  the  mixed  bromides  by  this  method  they  were  always 
completely  distilled  in  a  small  apparatus  which  was  so  con- 
structed that  it  was  relied  upon  for  retaining  all  of  the  bro- 
mides, while  it  was  hoped  that  the  distillation  would  free  them 
of  any  dissolved  propylene  or  hydrogen  bromide,  and  possibly 
other  impurities.     It  was  soon  found  that  very  small  amounts 
of  unknown  impurities  were  likely  to  shift  the  refractivity  so 
that  these  results  could  not  be  relied  upon  for  an  accuracy 
greater  than  10  to  15%,  as  shown  by  experiments  31  and  32. 
The  data  given  for  refractivity  are  thus  to  be  taken  with  this 
reservation;    but  there  are  few  cases  in  which  the  refractivity 
alone  is  depended  upon. 

3.  The  method  of  Michael  and  Leupold12  was  adopted  as  the 
most    practicable    for    obtaining    quantitative    results.     The 
mixed  bromides  are  shaken  in  sealed  tubes  with  an  aqueous  tenth 
normal  solution  of  silver  nitrate  for  three  hours  and  the  unused 
silver  nitrate  titrated  by  Volhard's  method.     In  this  time  all 
of   the  isopropyl  bromide  reacts  with  the  silver  nitrate,  while 
only  2.7%  of  the  normal  bromide  reacts  to  give  silver  bromide. 
A  single  blank  test  with  each  of  the  pure  bromides  was  in  per- 
fect agreement  with  the  results  of  Michael  and  Leupold. 

4.  The  products  were  shown  to  consist  practically  entirely 
of  propyl  bromide,   by  analysis  for  bromine  by  the  Carius 
method.     Some  of  the  results  are  low  by  about  2%  but  this 
can  be  ascribed  partly  to  the  difficulty  in  getting  the  last  traces 
of  silver  bromide  out  of  the  long  tubes. 

5.  When  a  sufficient  amount  of  the  mixed  bromides  was  at 
hand  it  was  submitted  to  a  fractional  distillation  in  a  still  of 
small   capacity,   constructed   similarly  to  those   of   Dufton.13 
The  fractionating  column  of  50  cm.  in  length  consisted  of  a 

11  V.  Meyer  Ann.,  171,  42  (1874);   Ber.,  8,  1073  (1875);   Ber.,  9,  384 
(1876). 

"Ann.,  379,  288(1911). 

11  /.  Soc.  Chem.  Ind.,  38,  45  (1919). 


11 

spiral  of  number  18  gage  constantan  wire  wound  tightly  around 
a  fine  glass  rod  of  0.3  cm.  diameter.  This  in  turn  fitted  tightly 
into  a  glass  tube  in  such  a  way  that  the  condensed  liquid  fol- 
lowed the  spiral  wire  in  returning  to  the  flask,  while  the  ascend- 
ing vapors  had  to  follow  the  spiral  space  between  the  wires. 
The  insulation  consisted  of  two  air  jackets  made  by  surround- 
ing the  column  with  increasingly  larger  pieces  of  glass  tubing. 
Isopropyl  bromide  boils  at  59-60°  C.  and  the  normal  bromide 
at  71.5°  C.  With  liquids  boiling  at  these  temperatures  the 
total  residue  remaining  in  the  still  after  everything  possible 
had  been  distilled  over,  usually  amounted  to  about  1.3  grams. 
The  still  was  tested  with  a  mixture  of  methyl  and  ethyl  alco- 
hols and  was  found  to  give  a  very  satisfactory  separation. 

It  was  believed  that  it  would  take  considerable  time  for  the 
gaseous  equilibrium  to  become  established  and  it  was  known 
that  reactions  of  this  type  are  frequently  very  susceptible  to 
the  presence  of  catalysts.  During  the  first  experiments  an 
attempt  was  therefore  made  to  find  some  substance  which  would 
have  the  desired  catalytic  effect.  The  presence  of  foreign 
materials,  however,  appeared  to  induce  decomposition  of  the 
bromides.  In  Table  I  a  few  results  with  catalysts  are  given. 
They  show  extensive  change  of  iso-  to  normal  propyl  bromide, 
but  no  agreement,  because  of  decomposition.  The  more  con- 
clusive experiments,  summarized  in  Tables  II  and  III,  were  all 
performed  in  pyrex  glass  tubes  (which  had  been  thoroughly 
cleaned  before  each  experiment  with  hot  bichromate  mixture), 
without  catalysts.  In  these  experiments  the  tubes  showed 
at  most  only  a  slight  coating  of  decomposition  products  and  the 
liquid  products  were  colorless  or  but  slightly  yellow;  this 
color  always  disappearing  entirely  upon  the  addition  of  potas- 
sium carbonate. 

The  mixed  bromides  were  analyzed  by  the  method  of  Michael 
and  Leupold.  The  percents  of  isopropyl  bromide,  as  given  in 
the  following  tables,  are  in  every  case  the  averages  of  duplicate 
determinations  which  usually  agreed  within  1%.  The  time 
required  for  the  escape  of  the  gases  into  the  condenser  is  given 
to  show  that  the  percentage  composition  of  the  bromides  was 
independent  of  this  time,  that  is,  the  condensation  of  the  bro- 
mides was  practically  complete. 


12 


Table  I 
Experiments  at  285-295°  C  with  Catalysts 

(Starting  with  i-propyl  Bromide) 


No.  of   Catalyst 
Exp.      present 

Time  of 
heating 

Time  for 
gases  to 
escape 

%  t-propyl 
bromide 

1        HgBr2 

4      days 

1  '20" 

46.8 

2       HgBr2 

3      days 

0'57" 

48.3 

3       Charcoal 

11      hrs. 

2'0" 

58.8 

4       BaBr2  • 

27.5hrs. 

0'53" 

Fractionated 

The  bromides  from  Experiment  4  were  fractionated  through 
the  small  spiral  still.  Although  with  the  small  amount  of 
liquid  the  fractionation  was  necessarily  imperfect,  the  presence 
of  the  normal  bromide  is  confirmed. 

Fraction      I  59 . 8  °  to  61 . 0  °  2.2  grams 

Fraction    II  61 .0°  to  64 .2°  0 .4  grams 

Fraction  III  64 . 2  °  to  70 . 3  °  0.7  grams 

The  residue  of  about  1.3  grams  was  probably  mostly  normal 
propyl  bromide. 

Table  II 
Experiments  at  285-2  95  °C  Without  Catalysts. 

(Starting  with  *-propyl  Bromide) 

Time  for 

No.  of  Time  of  gases  to  %  t-propyl 

Exp.  heating  escape  bromide          %  CaHyBr 

5  23. 5  hrs.  5'0"  67.9 

6  50      hrs.  2'9"  58.6  100.8 

7  71      hrs.  3'30"  54.7 

8  73. 5  hrs.  3'55"  53.3 


Table  III 
Experiments  at  285-2  95  °C  Without  Catalysts 

(Starting  with  n-propyl  Bromide) 

Time  for 

No.  of  Time  of  gases  to  %-t-propyl 

Exp.  Heating  escape  bromide         %CjH;Br 

9  ll^hrs.  15'    0"  47.6 

10  28      hrs.  1'20"  48.1 

11  49      hrs.  1'41*  52.2 

12  70      hrs.  4' 45"  54.3             97.9 

13  70      hrs.  3'    0"  54.7            98.1 

14  71      hrs.  T  30'  54.7             97.8 


13 

These  experiments  show  that  a  true  equilibrium  point  has 
been  reached,  starting  with  either  normal  or  isopropyl  bromide. 
This  equilibrium  is  attained  after  about  seventy  hours  heating 
at  285-295  °C.  Equilibrium  in  the  gaseous  phase  at  this 
temperature  exists  when  we  have  approximately  54.5%  of 
isopropyl  bromide,  that  is,  a  relatively  small  preponderance  of 
iso-  over  normal  propyl  bromide. 

Although  the  variation  of  the  equilibrium  point  with  tempera- 
ture should  be  slight,  in  consequence  of  the  very  small  difference 
in  the  heats  of  formation  of  such  isomers,  nevertheless  an  attempt 
was  made  to  determine  the  ratio  between  the  two  bromides  at 
equilibrium  at  a  lower  temperature.  A  few  of  these  results  are 
given  in  Table  IV. 

Table  IV 
Experiments  at  200  °C  Without  Catalysts    * 


Time  for 

o.  of 

Time  of 

gases  to 

;xp. 

Bromide  used 

Heating 

escape 

15 

f-propyl 

10  days 

2'  45" 

16 

i-propyl 

26  days 

4'  30" 

17 

w-propyl 

26  days 

5'  30" 

le 

74.6 
71.4 
15.0 

It  was  quite  apparent  that  the  equilibrium  position  had  not 
been  nearly  reached  from  either  end  and  no  further  experi- 
ments were  performed  at  this  temperature. 

II*  The  Union  of  Hydrogen  Bromide  With  Propylene 

Michael  believed  that  it  should  be  possible  to  draw  conclu- 
sions regarding  the  energy  relationships  of  two  isomeric  alkyl 
halides  from  data  showing  the  proportions  in  which  these  two 
isomers  were  formed  by  the  union  of  the  hydrogen  halide  with 
the  unsaturated  hydrocarbon.  However,  in  the  case  of 
hydrogen  bromide  and  isobutene,  it  was  found14  that  the  ratio 
of  the  velocites  of  formation  of  iso-  and  tertiary  butyl 
bromide  was  subject  to  great  variations  and  that  this  re- 
action was  greatly  influenced  by  catalytic  action. 

The  first  attempt  to  predict  which  of  two  isomers  would  be 
formed  by  such  a  reaction  was  the  empirical  rule  of  Markowni- 
koff15:  "When  an  unsymmetrical  hydrocarbon  combines  with  a 

"  /.  Amer.  Chem.  Soc.,  39,  1990  (1917). 
15  Ann.,  153,  256  (1870). 


14 


halogen  hydride,  the  addition  will  take  place  in  such  a  way  that 
the  halogen  is  joined  to  the  least  hydrogenated  carbon  atom; 
that  is,  to  that  carbon  atom  which  is  most  under  the  influence  of 
other  carbon  atoms".  Markownikoff  then  continues  and 
cites  among  other  examples  of  this  rule  the  addition  of 
hydrogen  iodide  to  propylene  as  giving  only  isopropyl  iodide. 
This  reaction  was  first  carried  out  by  Bertholet16  and  was  fur- 
ther studied  by  Erlenmeyer,17  Butlerow18  and  Michael.19 
The  latter  three  investigators  found,  besides  the  isopropyl 
iodide,  a  very  small  proportion  of  the  normal  iodide.  Michael 
believed20  that  in  the  propyl  bromides  formed  by  a  similar  re- 
action, the  proportion  of  normal  to  iso-propyl  bromide  would  be 
even  smaller  than  that  found  for  the  iodides.  However,  this 
has  not  been  found  to  be  the  case. 

In  the  following  experiments  it  will  be  shown  that  the  union 
of  hydrogen  bromide  and  propylene  is  also  subject  to  a  wide 
variation  which  is  probably  due  to  catalytic  action,  the  exact 
cause  of  which  has  not  been  ascertained.  However,  sufficient 
results  have  been  obtained  to  indicate  that  the  relative  ve- 
locities of  formation  bear  no  relation  to  the  relative  stabilities 
of  the  two  bromides  as  determined  in  Part  I  above. 

Reaction  in  the  Gaseous  State 

(a)  EQUIMOLECULAR  QUANTITIES  OF  PROPYLENE 
AND  HYDROGEN  BROMIDE  IN  LARGE  BULBS. 

The  procedure  followed  consisted  in  allowing  the  reaction 
to  take  place  in  a  large  bulb  or  flask.  The  bulb  was  evacuated 
and  heated  to  the  temperature  of  the  experiment.  Equal 
molecular  quantities  of  the  two  gases,  that  is,  one  half  atmos- 
phere of  each — as  measured  by  a  manometer  connected  to  a  pres- 
sure adjusting  device — were  introduced  at  the  beginning  of 
each  experiment.  The  pressure  in  the  bulb  was  rather  care- 
fully followed  during  the  course  of  the  reaction  by  means  of 
this  manometer.  In  some  cases  further  amounts  of  the  gases 
were  added  after  the  pressure  had  considerably  decreased.  In 

16  C.  R.,  54,  1350. 

17  Ann.,  139,228  (1866). 
»  Ann.,  145,275(1868). 

19  J.fur.  prakt.  Chem.,  60,  445  (1899). 

10  J.fiir.  prakt.  chem.  60, 447  (1899)  ;J.Am.  Chem.  Soc.,  32, 1004  (1910). 


15 


order  to  minimize  the  possibility  of  the  admission  of  air  into 
the  reaction  vessel  the  following  procedure  was  followed. 
All  connecting  tubes  were  first  evacuated.  The  propylene  was 
liquefied  (b.  pt.  —  50.2°C.)  in  a  small  bulb  surrounded  by  carbon 
dioxide  snow  and  ether.  This  bulb  was  then  attached  to  the 
evacuated  connecting  tubes,  placed  in  an  ice  and  salt  freezing 
mixture  and  permitted  to  boil,  the  gaseous  propylene  passing 
over  calcium  chloride.  A  stopcock  giving  an  outlet  to  the  air 
was  opened  and  the  propylene  was  boiled  until  there  was  a 
steady  flow  at  the  outlet  and  it  was  thought  that  any  residual 
air  had  been  swept  out  of  the  tubes.  This  stopcock  was  then 
closed  and  one  leading  to  the  bulb  opened.  Propylene  was 
boiled  into  the  bulb  until  the  pressure  measured  one  half  at- 
mosphere. An  almost  colorless  solution  of  hydrogen  bromide  in 
water,  saturated  at  the  temperature  of  an  ice  and  salt  freezing 
mixture,  was  connected  by  another  inlet  and  very  gently  warmed. 
The  solution  gave  off  hydrogen  bromide  which  was  dried  by 
passing  over  calcium  bromide  and  phosphorus  pentoxide. 
When  dense  fumes  appeared  at  the  open  outlet,  this  was 
closed  and  the  hydrogen  bromide  passed  into  the  bulb  until  the 
total  pressure  was  one  atmosphere. 

The  reaction  was  at  first  allowed  to  go  on  at  a  temperature 
which  was  sufficiently  high  to  keep  the  bromides  formed  in  a 
gaseous  state.  However,  it  was  soon  found  that  the  union 
took  place  but  slowly  at  these  temperatures  (80  to  130  °C.) 
and  some  experiments  were  tried  at  temperatures  as  low  as 
about21°C. 

Liquid  naturally  collected  in  the  bulbs  at  these  lower  tem- 
peratures and  it  was  thought  that  the  presence  of  a  liquid  sur- 
face might  exert  a  catalytic  effect  leading  only  to  the  formation 
of  one  of  the  two  possible  isomers.  This  had  been  found  to  be 
the  case  with  the  iso-  and  tertiary  butyl  bromides.  However, 
in  no  instance  was  it  found  possible  to  assign  any  definite  cat- 
alytic effect  to  the  presence  of  liquid  bromide,  though  the  cause 
of  the  extremely  wide  variation  in  the  composition  of  the  prod- 
ucts must  undoubtedly  be  sought  in  catalytic  action. 

But  little  liquid  product  could  be  obtained  from  the  3.3  liter 
bulb  which  was  first  used  and  only  one  of  these  experiments 
yielded  sufficient  product  to  test.  The  12  liter  bulbs  which 
were  used  in  a  large  majority  of  the  experiments  usually  gave 


16 

from  ten  to  fifteen  grams  of  the  mixed  bromides.  The  prod- 
ucts were,  in  general,  clean,  most  of  them  being  colorless  and 
the  rest  but  slightly  yellow;  this  color  disappearing  upon 
treatment  with  potassium  carbonate.  Several  of  the  products 
were  found  to  have  a  sharp  odor.  It  is  believed  that  this  odor  ap- 
peared whenever  slight  traces  of  some  unknown  impurity,  due 
probably  to  oxidation,  were  present,  since  it  was  noticeable  in 
products  which  gave  an  analysis  very  close  to  100%  for  C3H7Br. 
No  trace  of  this  odor  was  ever  noticed  in  the  products  of  any 
of  the  rearrangement  experiments.  However,  it  was  found 
that  when  the  tubes  from  these  experiments,  still  containing 
the  dissociated  gases,  were  left  open  to  the  air,  a  product  hav- 
ing this  characteristic  sharp  odor  was  formed. 

Expt.  18. — The  3.3  liter  bulb  was  evacuated  to  1.5  mm. 
pressure  and  heated  to  100  °C.  One  half  atmosphere  each  of 
hydrogen  bromide  and  propylene  were  introduced.  The  pres- 
sure decreased  more  regularly  than  in  most  of  the  later  ex- 
periments until  in  three  days  it  was  55.7  cm.  The  bulb  was 
then  removed  from  the  furnace  and  rapidly  cooled.  By  the 
refractivity  test  the  product  appeared  to  contain  76%  normal 
propyl  bromide. 

The  following  experiments  were  all  carried  out  in  12  liter 
pyrex  bulbs,  the  necks  of  which  were  drawn  down  and  sealed 
to  capillary  tubes  with  stopcocks. 

Expt.  19. — The  bulb  was  evacuated  to  1  mm.  pressure  and 
filled  as  in  Experiment  18  at  105  °C.  In  three  days  the  pres- 
sure had  decreased  to  about  54  cm.  and  appeared  to  be  re- 
maining almost  constant.  An  effort  was  therefore  made  to 
increase  the  reaction  velocity  by  warming  the  bulb.  The 
temperature  was  accordingly  gradually  raised  to  130  °C.  Six 
days  after  starting  the  experiment  and  at  a  pressure  of  60.8  cm. 
the  bulb  was  removed  from  the  furnace  and  quickly  cooled. 
The  liquid  product  was  washed  with  dilute  sodium  hydroxide 
solution  and  finally  with  water  and  then  dried  over  anhydrous 
potassium  carbonate  and  sodium  bromide.  The  liquid  un- 
doubtedly had  the  order  of  the  normal  bromide  and  gave  the 
nitrolic  acid  test  for  the  presence  of  a  normal  halide.  A  test 
by  the  refractivity  method  indicated  the  presence  of  p/%  of 
normal  propyl  bromide. 

The  major  portion  of  the  product  was  then  submitted  to  a 


17 

distillation  in  the  small  spiral  still.  It  was  found  impossible 
to  get  any  liquid  over  below  66.0°  C.  showing  that  the  percentage 
of  isopropyl  bromide  must  have  been  very  small  indeed.  Only 
two  fractions  were  taken:  I,  66.0 °C.  to  70.0 °C.  weighed  1.9 
grams;  while  II,  70.0°  C.  to  70.6°  C.  weighed  3.6  grams.  This 
latter  fraction,  plus  the  1.3  grams  of  residue  must  be  considered 
as  practically  pure  normal  propyl  bromide,  while  the  lower 
boiling  fraction  also  contained  a  large  proportion  of  the  higher 
boiling  isomer. 

Expt.  20. — This  experiment  was  carried  out  similarly  to  Ex- 
periment 19  except  that  the  temperature  was  kept  between 
133°  C.  and  200°  C.  in  an  effort  to  decrease  the  time  required. 
However,  the  pressure  decreased  very  slowly  and  in  fourteen 
days  after  a  total  decrease  of  only  13  cm.  it  was  found  that  con- 
siderable decomposition  had  taken  place  and  that  the  liquid 
had  a  sharp  odor.  The  refractivity  of  the  product  was  slightly 
beyond  that  of  the  pure  normal  bromide.  It  gave  a  nitrolic 
acid  as  shown  by  the  reddish  color  of  its  alkaline  salt,  also 
a  primary  nitro  compound  as  shown  by  the  copious  white  pre- 
cipitate with  lead  acetate. 

Expt.  21. — In  this  experiment  some  mercuric  bromide  was 
sucked  into  the  bulb  before  starting  the  experiment  in  the 
hope  that  this  might  definitely  catalyze  the  reaction.  The 
temperature  of  the  experiment  was  94  °C.  and  the  decrease  in 
pressure  17.1  cm.  Upon  removing  the  bulb  from  the  furnace 
it  was  noted  that  the  presence  of  foreign  material  had  produced 
the  same  results  as  in  the  rearrangement  experiments — namely : 
it  had  induced  a  great  deal  of  decomposition. 

Expt.  22. — No  catalyst  was  used  in  this  experiment  which 
in  other  respects  was  similar  to  the  preceding  ones.  The 
temperature  of  the  bulb  during  the  reaction,  which  lasted  for 
only  one  day,  was  125  °C.  In  this  time  the  pressure  had  de- 
creased 13.8  cm.  Upon  taking  the  bulb  out  of  the  furnace  it 
was  found  to  be  perfectly  clean  in  appearance  and  the  liquid 
which  collected  was  quite  clear  and  colorless.  The  product 
was  washed  with  dilute  sodium  hydroxide  and  water  and  then 
dried  over  fused  potassium  carbonate.  The  odor  was  that  of 
the  normal  bromide  with  a  slight  trace  of  the  sharp  smelling 
impurity.  The  product  gave  a  nitrolic  acid  as  determined  by 
its  reddish  yellow  alkaline  salt  and  a  nitro  compound  as  shown 


18 

by  the  copious  white  precipitate  with  lead  acetate.  The  ma- 
jor portion  of  the  product  was  put  through  the  small  spiral 
still  with  the  following  results : 

Fraction       I,  63  .0°-66  .0°  consisted  of  0.3  gram  (contained  sharp 
smelling  impurity). 

Fraction     II,  66  .0°-70.0°     consisted  of  0.5  gram. 
Fraction  III,  70.0 °-71 .0°     consisted  of  1.4  grams. 
Residue consisted  of  1 .3  grams. 

Expt.  23. — This  experiment  was  exactly  similar  to  the  pre- 
vious one  except  that  the  reaction  was  allowed  to  take  place  at 
room  temperature  in  a  room  which  was  usually  at  about  25°  C. 
in  the  day  time.  After  fourteen  days  during  which  time  the 
total  decrease  in  pressure  was  56.5  cm.,  it  was  found  that  the 
bulb  had  remained  perfectly  clean  with  no  trace  of  decompo- 
sition. The  liquid  was  purified  by  standing  over  anhydrous  po- 
tassium carbonate.  Analyses  were  made  by  the  method  of 
Michael  and  Leupold,  (loc.  cit.)  and  showed  the  presence  of 
55.8%  normal  propyl  bromide.  A  total  analysis  by  the  Carius 
method  was  carried  out  and  gave  a  somewhat  low  result  due  to 
the  overturning  of  the  crucible  containing  the  precipitate  to  be 
weighed.  It  was  known  that  a  small  amount  of  silver  bromide 
was  lost,  but  the  result  gave  97.61%  of  C3H7Br.  The  product 
must  have  been  practically  pure  C3H7  Br. 

Expt.  24. — In  this  experiment  the  mixed  gases  were  kept  at 
42°  C.  for  one  month  while  a  total  decrease  in  pressure  of  61.8 
cm.  was  noted.  Upon  cooling,  the  bulb  was  found  to  be  abso- 
lutely clean  and  there  was  no  trace  of  sharp  odor  to  the  product. 
It  was  left  standing  over  anhydrous  potassium  carbonate. 
This  was  analyzed  as  in  Experiment  23  and  gave  results  indi- 
cating the  presence  of  QQ.Q%  normal  bromide.  A  total  analysis 
gave  99.29%  of  C3H7Br.  The  liquid  was  put  through  the  small 
spiral  still  but  as  it  was  run  through  rather  too  rapidly  and  a 
thermometer  with  a  comparatively  large  bulb  was  used  the  re- 
sults were  not  very  good.  However,  over  80%  came  over  at  the 
boiling  point  of  normal  propyl  bromide. 

Expt.  25. — The  temperature  of  this  experiment  was  42 °C. 
After  seven  days  during  which  a  decrease  in  pressure  of  24.7  cm. 
had  taken  place,  the  bulb  was  removed  from  the  furnace.  No 
decomposition  or  charring  had  taken  place  but  the  sharp  odor 


19 


was  noticeable  in  the  liquid  product.  Analysis  gave  73.1% 
normal  propyl  bromide  and  99.56%  CsHyBr. 

Expt.  26. — In  this  experiment  one  half  atmosphere  each  of 
propylene  and  hydrogen  bromide  were  put  into  the  bulb  at 
room  temperature.  The  bulb  was  then  raised  to  80  °C.  and 
kept  at  this  temperature  for  six  days.  When  it  was  taken  out 
of  the  furnace  and  cooled,  only  a  very  small  amount  of  liquid 
collected — too  small  to  remove  for  analysis.  The  bulb  was 
opened  to  the  air  and  allowed  to  stand.  Four  days  later  it 
was  found  that  considerable  liquid  had  formed.  This  was 
undoubtedly  due  to  the  catalytic  effect,  probably  of  the  liquid 
layer,  possibly  of  something  which  had  entered  with  the  air. 
The  liquid  when  purified  with  fused  potassium  carbonate  had 
the  sari^£  sharp  odor.  This  could  not  have  been  due  to  un- 
saturated  products  as  a  test  with  a  dilute  bromine  solution 
showed  no  sign  of  the  existence  of  a  double  bond.  Analysis 
gave  75.42%  normal  propyl  bromide. 

Distillation  of  15.6  grams  of  this  product  through  the  small 
spiral  still,  the  temperature  being  followed  by  means  of  a  copper- 
constantan  thermo-couple,  gave  the  following  results : 

Fraction  I  59. 5°  to  61. 8°  1.6    grams  (f- propyl  bromide) 

Fraction  II  61 .8°  to  68.0°  2.7    grams 

Fraction  III  68 . 0  °  to  70 . 7  °  3.4    grams 

Fraction  IV  70 .7°  to  71 .5°  4 .45  grams  (w-propyl  bromide) 

Residue  1.3    grams 

Total  13.45 

(b)  IN  TUBES  AT  ATMOSPHERIC  PRESSURE  UNDER 
VARYING  CONDITIONS. 

In  these  experiments  the  apparatus  employed  by  Brunei21 
was  used.  The  gases  entered  separately  coming  to  temperature, 
mixing,  and  passing  on  through  the  tubes  together.  They 
were  then  cooled  by  passing  through  a  spiral  condenser  sur- 
rounded by  an  ice  and  salt  freezing  mixture.  This  experiment 
was  tried  at  various  temperatures  and  with  gases  of  varying 
degrees  of  moisture  and  purity.  The  tube  of  the  spiral  con- 
denser was  moistened  with  each,  in  turn,  of  the  propyl  bromides. 
However,  under  none  of  the  conditions  tried  did  the  union  take 
place  to  such  an  extent  that  anything  could  be  collected. 
21  /.  Amer.  Chem.  Soc.,  39,  1997  (1917). 


20 

REACTION  OF  PROPYLENE  AND  AQUEOUS   HYDRO- 
GEN BROMIDE 

(a)  GASEOUS    PROPYLENE   AT    ATMOSPHERIC 
PRESSURE. 

Many  attempts  were  made  to  absorb  propylene  by  aqueous 
solutions  of  hydrogen  bromide  under  atmospheric  pressure. 
The  original  idea  had  been  to  investigate  whether  or  not  the  liquid 
surface  would  so  catalyze  the  reaction  as  to  cause  the  forma- 
tion of  one — and  one  only — of  the  two  isomeric  propyl  bromides. 
Simple  as  this  reaction  would  at  first  glance  appear  to  be,  it 
was  found  to  be  accompanied  by  unexpected  difficulties — prob- 
ably due  to  unknown  catalytic  (" an ti -catalytic")  effects.  Most 
of  the  attempts  were  made  by  placing  a'queous  solutions  of 
hydrogen  bromide  in  a  flask  which  was  connected  to  ^  source 
of  propylene  (the  propylene  being  under  but  sligtmy  more 
than  atmospheric  pressure).  The  air  was  driven  out  of  the 
flask,  and  the  flask  was  placed  on  a  shaker  so  as  to  present  con- 
tinually a  fresh  surface  to  the  propylene.  Ground  glass  sur- 
faces were  also  tried  in  attempts  to  increase  the  absorbing  area 
and  thus  the  speed  of  formation  of  the  addition  products. 
It  was  necessary  to  avoid  hydrogen  bromide  solutions  of  con- 
centrations with  too  great  a  vapor  pressure  of  hydrogen  bro- 
mide, as  in  these  cases  the  gaseous  hydrogen  bromide  drove  the 
propylene  back  out  of  the  flask.  At  the  same  time,  if  the  solu- 
tion was  too  dilute  no  absorption  took  place.  Frequently 
the  solution  would  absorb  several  hundred  cubic  centimeters 
of  propylene  quite  rapidly,  and  then — for  no  reason  which 
could  be  determined  unless  it  were  due  to  dilution  of  the  solu- 
tion— would  stop.  Displacement  of  air  which  might  have  accu- 
mulated in  the  absorption  flask  did  no  good. 

Expt.  27. — This  was  the  only  one  of  these  experiments  which 
yielded  sufficient  product  to  test.  This  product,  after  wash- 
ing, and  drying  over  fused  potassium  carbonate  contained,  as 
found  by  the  refractivity  test,  p%  of  normal  propyl  bromide. 

Small  amounts  of  mercuric  bromide  and  aluminium  chloride 
were  added  to  solutions  of  hydrogen  bromide  in  the  hope  that 
they  might  have  a  favorable  catalytic  effect — but  without  suc- 
cess. 

Attempts  to  absorb  propylene  were  also  made  by  bubbling 


21 


the  gas  slowly  through  hydrogen  bromide  solutions,  and  by 
letting  the  gas  pass  slowly  up  through  a  long  column  filled  with 
pebbles,  down  through  which  a  solution  of  hydrogen  bromide 
was  slowly  dripping.  If  absorption  took  place  in  this  case  it 
was  only  to  so  small  an  extent  that  any  liquid  bromide  formed 
remained  on  the  pebbles  and  did  not  drain  down  into  the  re- 
ceiving flask. 

An  attempt  was  also  made  to  follow  the  method  used  for  the 
absorption  of  acetylene  in  sulfuric  acid,  using  mercuric  oxide 
as  catalyst,  as  given  by  Ullman.22  The  effort  was  made  in 
order  to  find  which  of  the  propyl  alcohols  would  be  formed  by 
this  reaction;  but  no  absorption  of  the  propylene  occurred. 

(6)  LIQIUD  PROPYLENE  IN  SEALED  TUBES. 

In  these  experiments  propylene  was  dried  by  passing  through 
calcium  chloride  tubes  and  was  liquefied  by  carbon  dioxide  snow. 
When  hydrogen  bromide  was  to  be  liquefied  the  drying  agents 
used  were  calcium  bromide  and  phosphorus  pentoxide.  The 
hydrogen  bromide  solutions  used  were  always  absolutely 
colorless,  and  appeared  to  give  perfectly  pure  propyl  bromides. 

Expt.  28. — Liquid  propylene  and  constant  boiling  aqueous 
hydrogen  bromide  were  sealed  in  a  tube  at  the  temperature  of 
carbon  dioxide  snow.  The  propylene  was  sufficient  to  react 
with  approximately  one  half  of  the  hydrogen  bromide.  This 
warmed  to  room  temperature  in  the  course  of  twelve  hours  and 
was  then  heated  to  36°  C.  to  complete  the  reaction.  On  open- 
ing there  was  but  slight  pressure  in  the  tube.  After  purifica- 
tion the  refractivity  test  showed  18%  of  normal  propyl  bromide, 

Expt.  29. — A  solution  of  hydrogen  bromide  saturated  at  the 
temperature  of  an  ice  and  salt  freezing  mixture  was  sealed  up 
with  enough  propylene  to  react  with  about  three  quarters  of  the 
hydrogen  bromide  in  the  solution.  This  was  finally  warmed 
in  water  at  50°  C.  From  the  pressure  observed  when  the  tube 
was  opened  this  appeared  to  contain  unused  propylene. 
Refractivity  indicated  the  presence  of  only  j%  normal  propyl 
bromide — and  this  may  mean  none  at  all. 

Expt.  30. — This  tube  contained  liquid  hydrogen  bromide  and 
an  excess  of  liquid  propylene  when  sealed.  On  opening  the 

22  Enzyklopadie  der  technischen  chemie,  1,  94  (1914). 


22 

excess  propylene  boiled  off.  The  refractivity  of  this  sample 
was  slightly  beyond  that  of  pure  isopropyl  bromide.  The 
boiling  point  was  57  °C.  In  the  presence  of  excess  propylene 
only  isopropyl  bromide  had  been  formed  and  none  of  the  primary 
isomer. 

Expts.  31  and  32. — These  experiments  are  duplicates  in  every 
respect  except  that  in  31  the  proportion  of  propylene  to  hydro- 
gen bromide  at  the  start  of  the  experiment  was  considerably 
greater  than  in  32.  Hydrogen  bromide  solution  saturated  at 
0°C.  and  liquid  propylene  were  sealed  in  these  tubes.  The 
products  were  washed  with  water  and  dried  over  fused  potas- 
sium carbonate.  The  results  of  these  experiments  were  as 
follows : 

No.  of  Analysis  with  Analysis  by 

Expt.  n/10  AgNOj  refractivity  %C»H:Br 

31  28.5%  n-propyl  bromide  12%  w-propyl  bromide  97.97 

32  35.5%  n-propyl  bromide  25%  n-propyl  bromide         100.7 

Most  of  the  product  from  31  was  distilled.  The  greater 
part  of  this  was  found  to  be  pure  isopropyl  bromide,  but  a  small 
amount  came  over  at  the  boiling  point  of  the  normal  bromide. 
The  distillation  was  run  through  too  quickly  for  quantitative 
results. 

A  part  of  the  product  from  32  was  also  distilled.  The  re- 
sults were  as  follows : 

Fraction       I  58.5°  to  60.0°  weighed  7.3  grams 

Fraction     II  60.0°  to  61.0°  weighed  8 . 9  grams 

Fraction  III  61.0°  to  66.5°  weighed  2 . 1  grams 

Fraction    IV  66.5°  to  71.0°  weighed  1 .2  grams 

Residue  weighed  1 .3  grams 

Expt.  33. — An  attempt  was  made  to  use  hydrogen  bromide 
solution  of  half  the  strength  of  those  used  in  31  and  32  but 
after  standing  for  several  days  the  tube  exploded. 

These  results  appear  to  indicate  that  if  the  formation  of 
one  or  the  other  isomer  is  not  entirely  dependent  upon  cataly- 
tic effects  which  have  not  been  determined  as  yet,  it  may  depend 
upon  the  relative  amounts  of  the  reacting  substances.  In 
Experiments  31  and  32  the  greater  ratio  of  hydrogen  bromide 
to  propylene  in  32  was  accompanied  by  formation  of  more  nor- 
mal propyl  bromide.  In  Experiments  28  and  29  the  relative 
values  (18:3)  of  the  normal  bromide,  although  determined  only 


23 

by  refractivity,  must  indicate  something;  and  in  this  case 
again  more  of  the  normal  propyl  bromide  has  been  formed  in 
that  case  where  the  ratio  of  hydrogen  bromide  to  propylene  is 
greater.  In  Experiment  30  a  large  excess  of  propylene  is  seen 
to  result  in  the  formation  of  only  isopropyl  bromide. 

These  results  when  compared  with  the  equilibrium  between 
the  bromides,  as  found  in  Part  I,  confirm  the  previous  statement 
that  there  is  no  relation  between  the  relative  stability  of  the 
compounds  in  question  and  this  relative  rates  of  formation 
from  hydrogen  bromide  and  propylene. 


Dissociation  of  the  Propyl  Bromides 

The  measurement  of  the  dissociation  of  the  propyl  bromides 
was  undertaken  by  the  method  used  for  the  butyl  bromides.23 
Contrary  to  Konowaloff,24  and  Michael  and  Zeidler  (loc.  cit.) 
there  was  no  difficulty  in  obtaining  dissociation,  although  very 
little  was  observed  at  the  temperatures  at  which  they  worked. 
As  the  addition  of  hydrogen  bromide  to  propylene  was  found  to 
go  more  slowly  than  with  isobutene,  so  the  dissociation  of  the 
propyl  bromides  always  required  at  least  several  days  as  com- 
pared with  the  few  hours  required  for  the  butyl  bromides  to  reach 
a  state  of  equilibrium.  Owing  to  the  long  heating  required  the 
decomposition  was  frequently  so  great  that  good  results  could 
not  be  obtained,  and  thus  the  dissociation  constants  are  only 
approximate.  They  are,  however,  surprisingly  close  to  those 
found  for  the  butyl  bromides.  Catalysts,  when  tried,  were  found 
to  induce  decomposition,  rather  than  to  aid  the  dissociation. 

In  the  following  tables  the  calculated  pressure  (P  calc.)  is 
that  pressure  which  the  amount  of  bromide  used  in  a  given  ex- 
periment would  exert  at  the  temperature  of  the  experiment, 
provided  that  there  were  no  dissociation.  In  the  last  column 
the  per  cent  dissociated  is  indicated  by  the  excess  of  the  values 
over  100.  The  dissociation  constant  is  represented  by  K. 

Expt.  34.  —  No  catalyst  was  present  in  the  bulb  during  this 
experiment. 

2.701  grams  of  isopropyl  bromide  were  used  in  a  vapor  density  bulb 
of  1131  c.c.  capacity  at  25°  C. 

23  /.  Amer.  Chem.  Soc.,  39,  1978  (1917). 

24  Ber.,  18,  2808  (1885). 


24 

Time  Temp.  P  obs.  P  calc.  100  P  °bs' 


P  calc. 

1  hr. 

124° 

47.66 

48.07 

99.15 

5hrs. 

152° 

51.52 

51.46 

100.1 

11  hrs. 

191° 

58.36 

56.18 

103.9 

16  hrs. 

229° 

63.31 

60.78 

104.2 

21  hrs. 

237° 

68.5 

61.75 

110.2 

39  hrs. 

296° 

111.20 

68.88 

161.4 

45  hrs. 

296° 

118.38 

68.88 

171.9 

58  hrs. 

301° 

118.01 

69.50 

169.8 

65  hrs.  121°  48.15  47.71  100.9 

At  296°  C.:  per  cent  dissoc.  =  71 .9;  K  =0.03572. 

It  is  to  be  noted  that  after  only  seven  hours,  at  a  lower  tem- 
perature at  the  end  of  the  experiment,  the  dissociation  prod- 
ucts had  almost  completely  recombined. 

Expt.  35. — In  this  experiment  mercuric  bromide  was  present 
in  the  vapor  density  bulb  as  a  catalyst.  In  every  case  the  pres- 
sure given  as  the  observed  pressure  is  the  obesrved  total  pressure 
in  the  bulb  minus  the  calculated  pressure  of  the  mercuric  bro- 
mide ;  that  is,  it  is  the  observed  pressure  of  the  propyl  bromides 
and  their  dissociation  products. 

2.379  grams  of  isopropyl  bromide  were  used  in  a  vapor  density  bulb 
of  1218.550  c.c.  capacity  at  25°  C. 

Time  Temp.  P  obs.  P  calc.  100 


3  hrs. 

134° 

40.78 

40.29 

101.2 

17  hrs. 

312° 

100.36 

57.91 

173.3 

28  hrs. 

301° 

98.12 

56.82 

172.7 

47  hrs. 

299° 

99.13 

56.62 

175.1 

52  hrs. 

129° 

67.14 

39.80 

168.7 

64  hrs. 

126° 

63.09 

39.50 

159.7 

At  299°  C.:  per  cent  dissoc.  =75.1;   K  =  0  03874. 

In  this  experiment,  after  seventeen  hours  at  a  temperature 
near  126°  C.  at  the  end  of  the  experiment,  very  little  recombina- 
tion had  occurred. 

Due  to  the  low  molecular  weight  of  the  substance  under  in- 
vestigation so  little  of  the  material  could  be  used  in  the  vapor 
density  bulbs  that  it  was  impossible  to  get  any  liquid  out  of 
them  at  the  completion  of  an  experiment  for  analytical  purposes. 

In  general  the  results  of  these  experiments  did  not  agree 
well  and  only  the  two  most  reliable  ones  have  been  given. 


25 


PREPARATION  OF  MATERIALS 

The  hydrogen  bromide  used  throughout  this  research  was 
made  catalytically  by  bubbling  electrolytic  hydrogen  through 
bromine,  kept  at  about  40  °C.,  and  passing  the  mixed  gases 
through  a  quartz  tube,  partially  filled  with  platinized  asbestos 
and  electrically  heated  to  a  red  heat.  With  the  exception 
of  one  rubber  stopper  at  the  entrance  to  the  quartz  tube, 
there  were  no  rubber  connections  on  the  apparatus.  Phos- 
phoric acid  was  used  as  lubricant  in  the  stopcocks  and  ground 
glass  joints.  The  apparatus  gave  colorless  solutions  of  hy- 
drogen bromide. 

Isopropyl  alcohol,  was  prepared  by  the  reduction  of  acetone 
under  pressure,  using  nickel  oxide  as  catalyst.  The  method  is 
that  of  Ipatiew26  as  used  by  Brunei,  Crenshaw,  and  Tobin.26 
The  alcohol  was  then  dried  over  lime  and  fractionated  through 
tall  Hempel  columns. 

Isopropyl  bromide  was  made  from  hydrogen  bromide  and 
isopropyl  alcohol,  in  the  main  according  to  N  orris.27  The 
alcohol  was  quickly  poured  into  a  saturated  hydrogen  bromide 
solution.  A  steady  stream  of  hydrogen  bromide  was  kept 
bubbling  through  the  solution.  The  heat  of  the  reaction,  to- 
gether with  the  stream  of  hydrogen  bromide  was  sufficient  to 
carry  the  greater  portion  of  the  bromide  formed  up  through  a 
Hempel  column. 

The  reaction  mixture  was  finally  warmed,  but  it  was  not 
necessary  at  any  time  to  boil  it.  The  bromide  was  collected 
under  water,  washed  with  dilute  sodium  hydroxide  and  water, 
dried  over  calcium  chloride  and  phosphorus  pentoxide,  and 
fractionated. 

The  normal  propyl  bromide  used  in  this  research  had  been 
made  and  fractionated  previously  but  was  refractionated  be- 
fore using. 

The  propylene  was  prepared  according  to  the  method  of 
Freund28  by  dropping  isopropyl  iodide  upon  a  mixture  of  alco- 
holic potassium  hydroxide  and  powdered  potassium  hydroxide 

25  C.A.,  1,2878  (1907). 

26  J.  Amer.  Chem.  Soc.,  43,  561  (1921). 
•>--  A.  C.  J.,  38,  637  (1907). 

28/.,  400,  (1882). 


26 

in  a  Michael  retort.29  To  every  part  of  iodide,  one  part  by 
weight  of  a  one  to  three  alcoholic  solution  of  potassium  hydrox- 
ide and  in  addition  to  this  one  half  part  by  weight  of  powdered 
potassium  hydroxide  were  used.  One  half  mole  of  the  iodide 
gave  a  little  over  eleven  liters  of  propylene  at  room  temperature. 
The  propylene  was  collected  and  kept  over  water  in  glass 
gasometers. 

The  isopropyl  iodide  used  in  the  above  preparation  was  made 
according  to  the  directions  of  Adams,  Kamm  and  Marvel.30 

Summary 

The  equilibrium  between  normal  and  isopropyl  bromides 
and  their  dissociation  products,  hydrogen  bromide  and  propy- 
lene, at  290  °C.,  has  been  studied.  The  ratio  determined  was 
54.7%  of  isopropyl  bromide  to  45.3%  of  normal  propyl  bromide. 

It  has  been  shown  that  catalytic  influences  come  into  play 
in  the  formation  of  these  bromides  from  hydrogen  bromide  and 
propylene,  so  that  reaction  between  the  gases  usually  gives 
almost  entirely  normal  propyl  bromide,  even  in  the  presence  of 
a  liquid  surface;  while  the  reaction  of  liquid  propylene  with 
liquid  or  aqueous  hydrogen  bromide  always  gives  at  least  a 
large  proportion  of  isopropyl  bromide. 

A  dissociation  constant  has  been  determined  for  the  propyl 
bromides  and  this  has  been  found  to  be  of  the  same  order  of 
magnitude  as  that  of  the  butyl  bromides. 

29  Ber.,  34,  4958  (1901). 

30  Univ.  of  111.  Bull,  XVI,  21  (1919). 


VITA 

I,  Helen  Goldstein  Rafsky,  was  born  in  New  York  City  in 
1897.  My  parents  are  Albert  Sigmund  Goldstein  and  Char- 
lotte Frank  Goldstein.  I  attended  the  Training  Department 
of  Hunter  (then  Normal)  College  and  the  Hunter  College  High 
School  until  1914,  when  I  entered  Barnard  College.  In  1918 
I  received  a  B.S.  degree  from  Barnard  College,  Columbia  Uni- 
versity. From  1918  to  1919  I  was  Scholar  in  Chemistry  at 
Bryn  Mawr  College;  from  1919  to  1921,  Fellow.  From  1921 
to  1922  I  was  Helen  Schaeffer  Huff  Memorial  Research  Fellow. 

My  preliminary  examinations  for  the  Ph.D.  degree  were 
taken  in  November  1921.  My  major  subject  was  Organic 
Chemistry  under  Dr.  Roger  Frederick  Brunei;  my  associate 
minor  was  Physical  Chemistry  under  Dr.  James  Llewellyn 
Crenshaw;  and  my  independent  minor,  Physics,  under  Dr. 
James  Barnes.  I  wish  to  express  my  sincere  appreciation  of 
the  very  able  instruction  I  have  received  from  these  prof essors 
and  of  their  continued  interest  in  my  work. 

In  conclusion,  I  wish  to  state  that  the  investigation  de- 
scribed in  the  preceding  pages  was  undertaken  at  the  sug- 
gestion of  Professor  Brunei  and  carried  out  under  his  direction. 
I  feel  that  whatever  merit  the  work  may  possess  is  due  to  his 
kindly  interest  and  careful  direction,  and  I  desire  to  express  my 
appreciation  of  his  valuable  instruction. 


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